They are equivalent because of a cultural difference. In Spanish you count the current day when you discuss time lapses. So, while in English we would say “in one week” in Spanish you would say “de hoy en ocho” which roughly translates to “from today in eight (days)” where the word “days” is implied. The same goes for two weeks. In English it is viewed as in 14 days while in Spanish you would count the current day and say in 15.